Selectivity assessment of a sequential extraction procedure for metal mobility characterization using model phases

This study considers the selectivity of the extractants used in a sequential extraction scheme for metals mobility assessment by analyzing individual mineral phases previously coprecipitated or sorbed with trace metals. The scheme evaluated was a modification of the Tessier et al. [A. Tessier, P.G.C. Campbell, M. Bisson, Anal. Chem. 51 (1979) 844] sequential procedure proposed by the authors. The phases studied were calcite, amorphous iron oxide, hausmannite, humic acid, kaolinite and illite. Selective extractions were obtained for As, Cr, Cu, Ni, Pb and Zn in metal-coprecipitated phases whereas NH(2)OH-HCl was not selective for the extraction of Hg and Cd coprecipitated in hausmannite and amorphous iron oxide, respectively. Otherwise, Cd, Hg, Ni and Zn sorbed on the different phases were released with MgCl(2) and NaOAc/HOAc, but stronger reagents were needed to release As, Cr, Cu and Pb.     

Fractionation of lead in soils affected by smelter activities using a continuous-flow sequential extraction system

A continuous-flow sequential extraction system was used to study the distribution of Pb, and its association with other elements (Fe, Al and Ca), in soils around a Pb smelter. Soil samples were analysed by a four-step continuous-flow sequential extraction procedure employing a modified Tessier/BCR scheme. Recoveries of Pb using the flow system (88–111%) were higher than those obtained using a conventional batch extraction system. There were also some differences in Pb distribution between fractions as determined using the two extraction systems. The most abundant fraction of Pb was extracted during the dissolution of soil oxides (Fe/Al). Extractograms (plots of concentration of elements vs. extractant volume/time) indicated that anthropogenic Pb was predominantly adsorbed onto Fe oxide surfaces in contaminated soils. In soil profiles, the highest amounts of Pb were found in the topsoil surface layers (0–5?cm) of the contaminated soils with only limited movement into subsurface layers.     

Metal fractionation in olive oil and urban sewage sludges using the three-stage BCR sequential extraction method and microwave single extractions

The conventional three-stage BCR sequential extraction method was employed for the fractionation of heavy metals in sewage sludge samples from an urban wastewater treatment plant and from an olive oil factory. The results obtained for Cu, Cr, Ni, Pb and Zn in these samples were compared with those attained by a simplified extraction procedure based on microwave single extractions and using the same reagents as employed in each individual BCR fraction. The microwave operating conditions in the single extractions (heating time and power) were optimized for all the metals studied in order to achieve an extraction efficiency similar to that of the conventional BCR procedure. The measurement of metals in the extracts was carried out by flame atomic absorption spectrometry. The results obtained in the first and third fractions by the proposed procedure were, for all metals, in good agreement with those obtained using the BCR sequential method. Although in the reducible fraction the extraction efficiency of the accelerated procedure was inferior to that of the conventional method, the overall metals leached by both microwave single and sequential extractions were basically the same (recoveries between 90.09 and 103.7%), except for Zn in urban sewage sludges where an extraction efficiency of 87% was achieved. Chemometric analysis showed a good correlation between the results given by the two extraction methodologies compared. The application of the proposed approach to a certified reference material (CRM-601) also provided satisfactory results in the first and third fractions, as it was observed for the sludge samples analysed.     

The certified reference materials CRM 142 R light sandy soil, CRM 143 R sewage sludge amended soil and CRM 145 R sewage sludge for quality control in monitoring environmental and soil pollution

The determination of various heavy metals in soils and sludges provides an indication for their degree of contamination. Therefore the reliability of such determinations is of utmost importance. Quality assessment can be performed by using adequate certified reference materials. Because of their success, the present supplies of the BCR CRM 142, CRM 143 and CRM 145 are exhausted. The Measurement and Testing Programme (BCR) of the Commission of the European Communities decided to replace them. After a careful preparation procedure of materials sufficiently similar to the exhausted ones and a homogeneity and stability study, the new materials were certified for a series of trace elements also including their aqua regia soluble fraction. Indicative values for other elements are given as well.     

Evaluation of a sequential extraction procedure for the determination of extractable trace metal contents in sediments

The determination of extractable trace metals in sediments using sequential extraction procedures has been performed in many laboratories within the last ten years in order to study environmental pathways (e.g. mobility of metals, bounding states). However, the results obtained by different laboratories could hardly be compared due to lack of harmonized schemes. Owing to the need for standardization and subsequent validation of extraction schemes for sediment analysis, the Measurements and Testing Programme (formerly BCR Programme) of the European Commission has organized a project to adopt a sequential extraction procedure that could be used as a mean of comparison of data of extractable trace metals in sediments. A scheme was designed after a series of investigations on existing schemes and tested in interlaboratory studies. This paper presents the results of two round-robin exercises on extractable trace metals using this sequential extraction protocol and describes the final version of the extraction procedure amended according to the most recent improvements.     

Effects of freeze-drying on partitioning patterns of major elements and trace metals in lake sediments

The effect of freeze-drying on elemental partitioning pattern in four lake sediments was evaluated using the sequential extraction method developed under the auspices of Community Bureau of Reference (BCR) of the Commission of European Communities. Redox-sensitive elements like iron, manganese, phosphorus, and sulfur were analyzed simultaneously with several trace metals. This allows a qualitative determination of which trace metal-scavenging phases commonly found in freshwater sediments that are most susceptible to freeze-drying.The comparison of a surface layer and a deeper more reduced layer collected from four sediment cores ranging from sub-oxic to anoxic condition indicate the changes in partitioning pattern due to freeze-drying. Two of the lakes exhibiting clearly reduced environments are most affected by freeze-drying in terms of change in partitioning patterns. However, this effect is element specific and varies with sediment depth along the redox gradient. Elements commonly associated with a sulfide phase (S, Fe, Cu, Zn, and Pb) and extracted in BCR step 3 are the most affected elements, but at the same time also dependent on the organic matter content in the sediment. Si and Al that are often considered as conservative elements show a shift from step 3 to step 2, and it is interpreted as a release of Si and Al from organic matter and the subsequent formation of oxides during freeze-drying. Calcium and manganese, elements that are often associated with a carbonate phase, do not seem to be severely affected by this kind of treatment. Carbonate-associated iron (operationally defined), however does show a clear tendency to oxidize during the freeze-drying process. In fact, the shift in iron (carbonate to oxide fraction) corresponds to 3-4% (w/w) of the total sediment in some cases. Surprisingly, a significant fraction of iron originally extracted in step 1 (as “carbonate”) seems to be immobilized during freeze-drying.These results clearly show that freeze-drying does not preserve the speciation pattern of major elements, trace metals, phosphorus, and sulfur in anoxic lake sediment core sections during storage prior to BCR sequential extraction procedures.     

Speeding up of a three-stage sequential extraction method for metal speciation using focused ultrasound

The three-stage sequential extraction procedure, proposed by the European Community Bureau of Reference (BCR), has been applied for speciation of copper, chromium, nickel, lead and zinc in a sludge sample collected from an urban wastewater treatment plant. The conventional BCR sequential extraction method has been modified, in each stage, applying ultrasonic energy by means of a probe (handling at an adequate sonication power and time) in order to shorten the required operation time. Extractable metal contents obtained by both the conventional and the accelerated ultrasonic extraction method, were measured by Flame-Atomic Absorption Spectrometry. Results obtained in each fraction by both methods were statistically compared (P=0.95) for all the studied elements and no significant differences were found except for chromium and zinc in the third fraction (oxidisable). For all metals the extraction percentage was>95%. The proposed accelerated sequential extraction method could be a valid alternative to the conventional shaking with a much shorter operating time.     

Investigation of heavy metals mobility in shrimp aquaculture sludge—Comparison of two sequential extraction procedures

Influence of heavy metals was investigated by conducting various tests on the samples collected from aquaculture shrimp in Selangor, Malaysia. The concentration of heavy metals in the sludge and potential of mobility based on its association forms was studied. Two sequential extraction methods (five stages Tessier method and three steps BCR method) were used to determine the binding forms of the metals.From the analysis, Ca, Fe and Mn were found to be highest concentrated metals compared to Zn, Cu, Cr, Cd and Pb in aquaculture shrimp sludge. From the sequential extraction, Cd, Mn and Pb were mostly found in exchangeable/carbonate form, showed its susceptibility to be leached easily. Also Cu and Zn were extracted predominantly in oxidizable form. All metal concentrations (except Cd, Zn and Cu) were extracted to be higher in residual fraction in this method. The results of BCR method are totally similar to the five stages Tessier method. By comparing the percent of recovery, the BCR method was better than Tessier method. Nevertheless for both methods the percent of their recoveries were acceptable. For Pseudototal metal digestion, although the concentration of Cd is less than other heavy metals, it is very harmful as a fertilizer because Cd is one of the heavy metals that might be in the leaf or fruit of plants. Also for investigation of Ca in the sludge, this element was measured and high amounts of that show sludge is useful for growing of plant. The results of direct digestion of heavy metals show that with the control of Cd in this sludge we can use this sludge as fertilizer in soils for agriculture but it is better if it is used for fruitless plants.     

Determination of molybdenum in extracts of soil and sewage sludge CRMs after fractionation by means of BCR modified sequential extraction procedure

A modified three-step sequential extraction procedure proposed by the Commission of European Communities Bureau of Reference (BCR) was applied to certified reference materials of three different soil groups (rendzina, luvisol, and cambisol) and sewage sludge of different compositions originating from a municipal water treatment plant in order to assess potential mobility and the distribution of molybdenum in the resulting fractions. In the soils examined, molybdenum was present almost entirely in the mineral lattice, the content of molybdenum in the fractions of the studied reference materials of sludges was predominant in the fraction, represents Mo bound to organic matter and sulphide.The internal check of accuracy was performed on the results of the sequential extraction by comparing of the extractable amounts of molybdenum in the sequential procedure with the results of the pseudototal digestion of original samples. The recovery ranged from 96 to 101% and the precision (RSD) in the extracts was below 10%.     

Comparison of Two Sequential Extraction Procedures for Trace Metal Partitioning in Sediments

Abstract

Two sequential extraction schemes (a modified Tessier procedure with five steps and a three steps protocol designed by BCR) are applied to four sediment samples with different heavy metal contents. The results obtained for Cd, Cr, Cu, Ni, Pb and Zn partitioning show that the metal distribution obtained with both procedures are significantly different. With the second procedure amounts of all the heavy metals are extracted with the oxidizing reagent (third fraction) whereas with the first one the non residual metals are distributed among the second, third and fourth fractions (acetic acid-acetate buffer (pH=5), reducing and oxidizing reagents respectively). The residual fraction obtained applying the three steps procedure is in general higher than that obtained using the five steps procedure, except for cadmium.     

Critical evaluation of novel dynamic flow-through methods for automatic sequential BCR extraction of trace metals in fly ash

Two novel dynamic extraction approaches, the so-called sequential injection microcolumn extraction and sequential injection stirred-flow chamber extraction, based on the implementation of a sample-containing container as an external extraction reactor in a sequential injection network, are for the first time, optimized and critically appraised for fractionation assays. The three steps of the original Community Bureau of Reference (BCR) sequential extraction scheme have been performed in both automated dynamic fractionation systems to evaluate the extractability of Cr, Cu, Ni, Pb, and Zn in a standard reference material of coal fly ash (NIST 1633b). In order to find the experimental conditions with the greatest influence on metal leachability in dynamic BCR fractionation, a full-factorial design was applied, in which the solid sample weight (100–500 mg) and the extraction flow rate (3.0–6.0 mL min⁻¹) were selected as experimental factors. Identical cumulative extractabilities were found in both sequential injection (SI)-based methods for most of assayed trace elements regardless of the extraction conditions selected, revealing that both dynamic fractionation systems, as opposed to conventional steady-state BCR extraction, are not operationally defined within the selected range of experimental conditions. Besides, the proposed automated SI assemblies offer a significant saving of operational time with respect to classical BCR test, that is, 3.3 h versus 48 h, for complete fractionation with minimum analyst involvement. Schematic illustration of automatic flow-based setups for dynamic fractionation of trace metals in fly ash

Determination of bioavailable fractions of Zn, Cu, Ni, Pb and Cd in soils and sludges by atomic absorption spectrometry

The single extraction procedures validated by the standards, measurement and testing programme (formerly BCR), extraction with 0.05 mol l⁻¹ EDTA and 0.43 mol l⁻¹ acetic acid, have been applied to reference materials of soils and sludges with certified total values of elements, in order to determine bioavailable contents of Cd, Cu, Ni, Pb and Zn. These soils, which represent uncontaminated pedologically different types of soils from Slovakia and sludges from city water treatment are characterized for the bioavailable fraction of the metals using the procedures followed by SM&T Programme. Concentrations of the elements under the study in the extracts were determined by flame (FAAS) using calibration curves in appropriate extractants and by electrothermal (ETAAS) atomic absorption spectrometry, using technique of standard additions for the evaluation of the results. The accuracy of the extraction procedures and determinations of the elements in the extracts was controlled using CRM 483 certified for EDTA- and acetic acid-extractable contents of Cd, Cu, Ni, Pb and Zn in sewage sludge amended soil.     

A comparison of an optimised sequential extraction procedure and dilute acid leaching of elements in anoxic sediments, including the effects of oxidation on sediment metal partitioning

The effect of oxidation of anoxic sediment upon the extraction of 13 elements (Cd, Sn, Sb, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) using the optimised Community Bureau of Reference of the European Commission (BCR) sequential extraction procedure and a dilute acid partial extraction procedure (4 h, 1 mol L⁻¹ HCl) was investigated. Elements commonly associated with the sulfidic phase, Cd, Cu, Pb, Zn and Fe exhibited the most significant changes under the BCR sequential extraction procedure. Cd, Cu, Zn, and to a lesser extent Pb, were redistributed into the weak acid extractable fraction upon oxidation of the anoxic sediment and Fe was redistributed into the reducible fraction as expected, but an increase was also observed in the residual Fe. For the HCl partial extraction, sediments with moderate acid volatile sulfide (AVS) levels (1-100 μmol g⁻¹) showed no significant difference in element partitioning following oxidation, whilst sediments containing high AVS levels (>100 μmol g⁻¹) were significantly different with elevated concentrations of Cu and Sn noted in the partial extract following oxidation of the sediment. Comparison of the labile metals released using the BCR sequential extraction procedure (ΣSteps 1-3) to labile metals extracted using the dilute HCl partial extraction showed that no method was consistently more aggressive than the other, with the HCl partial extraction extracting more Sn and Sb from the anoxic sediment than the BCR procedure, whilst the BCR procedure extracted more Cr, Co, Cu and As than the HCl extraction.     

Comparative study of optimised BCR sequential extraction scheme and acid leaching of elements in the certified reference material NIST 2711

The optimised BCR sequential extraction procedure and a 4 h 1 mol L⁻¹ HCl partial extraction have been performed on the NIST 2711 reference material for a suite of 12 elements (Cd, Sb, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) using magnetic sector ICP-MS. A pseudo-total aqua regia digest of NIST 2711 has also been undertaken for quality assurance purposes, and comparison of the sum of the four BCR fractions, which included an aqua regia digest on the residue, with the pseudo-total aqua regia digest has been used to assess the accuracy of the BCR partitioning approach. As a result of this work, discrepancies between previous studies about BCR partitioning of elements in NIST 2711 have been discussed and an increase in confidence about the use of BCR partitioning scheme on seven elements (Cd, Pb, Al, Mn, Fe, Cu, Zn) in this standard material has been obtained. On the other hand, BCR partitioning for Sb, Cr, Co, Ni and As has been provided for the first time. Partial extraction results are also reported for the same 12 elements analysed by the optimised BCR procedure, with the partial extraction results exhibiting a strong correlation with the sum of the three labile steps of the BCR procedure.     

Different strategies to assess Cu and Pb mobilization in polluted river sediments

Summary For studying the mechanisms of trace metal mobilization in sediments several strategies have been employed, such as single extraction, sequential extractions, ion exchange, or progressive acidification. Several authors assert that sequential extraction is the best option. In this study two procedures are used in order to assess the mobility of copper and lead in heavily polluted river sediments: sequential extraction using a modified Tessier procedure, and progressive acidification, using an automated method. Six heavily polluted sediment samples are studied by applying the two procedures. The amount of metal released at different pH-values (pH 5 and pH 2) is compared with the resulting distribution when the sequential extraction procedure is applied. The information obtained from the two different approaches is discussed. For both metals a different behaviour is observed when applying each of the two procedures. Thus, copper is more easily released than lead when progressive acidification is followed, whereas an inverse situation is observed when sequential extraction is applied.     

Assessment of heavy metals leachability from metallo-organic sorbent-iron humate-with the aid of sequential extraction test

The sequential extraction test, known as a BCR procedure, was used to assess a leachability of heavy metals (Zn, Cd, Pb, Cu) from the metallo-organic sorbent—iron humate—loaded with these metals. The sequential test allowed to discriminate between various fractions of heavy metals, namely the acid-extractable fraction, the fraction bound to Fe oxides, and the fraction bound to organic matter. It was proven that the heavy metals are bound mainly to Fe oxides and organic matter, and thus they may be relatively hardly liberated into the environment. The BCR sequential extraction test exhibited a very good repeatability, when it was applied to the loaded sorbent—relative standard deviations were typically lower than 10%.     

Mercury determination in solid phases from application of the modified BCR-sequential extraction procedure: a valuable tool for assessing its mobility in sediments

The present paper presents a feasibility study for the evaluation of mercury mobility in sediments by application of the modified BCR three-step sequential extraction procedure (BCR-SEP). The aim of the study was to evaluate the effect of acidification, reduction and oxidation processes on mercury mobility from sediments, once the SEP was validated with other trace metals.As extractable mercury amounts were mostly found below detection limits of the advanced mercury analyser (AMA-254) used for measuring the extracts (L.D.<0.5 ng), the use of a solid sampling atomic absorption spectrometer with a specially designed furnace for Hg atomisation was found to be an optimal technique to quantify Hg in the solid residues coming from the SEP.With this approach, mercury was found to be hardly mobile and only for one of the moderately polluted sediments (BCR CRM 320), extractable mercury (exchangeable fraction, BCR procedure step 1) has been found. An oxidation step with H(2)O(2) was required to obtain extractability up to 64% of the total content in a highly polluted lagoon sediment.     

Comparison of three sequential extraction procedures (original and modified 3 steps BCR procedure) applied to sediments of different origin

The 3 steps sequential extraction procedure proposed by the Standards Measurements and Testing program (SM&T--formerly BCR) of the European Union has been applied for the speciation of metals in sediments. Results obtained by the application of the BCR standardized procedure were compared to those of two four step sequential extraction procedures, which are different from the BCR procedure only for the introduction of an additional step with NaOCl, as 2nd and 3rd step respectively. Five different metals have been taken into consideration: Cd, Cu, Ni, Pb and Zn. The analytical performances of the laboratory have been evaluated using three certified reference materials: the BCR 601 lake sediment for the BCR sequential extraction procedure, PACS-1 and MESS-1 for total metal concentration. Results showed that the efficiency of NaOCl treatment is higher or at least equal to that of H2O2 treatment and that its selectivity is quite satisfying. Moreover the NaOCl treatment doesn't significantly influence the extraction of the easily reducible fraction.     

Mobility of important toxic analytes in urban dust and simulated air filters determined by sequential extraction and GFAAS/ICP-OES methods

The modified BCR three-step sequential extraction procedure has been applied to homogenized urban dust samples and to simulated air filters loaded with the prepared urban dust via the wet deposition procedure. This work has been focused on comparative study of the distribution of trace elements in both samples and evaluation of the factors influencing the reliability of results with respect to the proposed extraction procedure. Extracted chemical fractions were analyzed by ICP-OES and GFAAS depending on the concentration levels of investigated trace elements As, Cd, Cr, Mn, Ni, and Pb, selected according to their adverse effect on the human health. Statistically evaluated results indicate significant differences between the extracted portions of analytes in urban dust and simulated air filters, where the mobility of some analytes in simulated air filters was higher than that in urban dust samples. The impact of surfactant Triton X-100 (0.05 vol. %) on the extraction procedure was also investigated. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Methodological study of extraction procedures applied to urban particulate matter

The modified BCR three-step sequential extraction procedure has been applied to two different samples of urban particulate matters (PM). The distribution of selected trace elements As, Cd, Cr, Mn, Ni, Pb, Zn was investigated and, in a comparative study, the presence of common organic air filters in extraction procedures was evaluated. Analytes in separate fractions were determined by ICP-OES and GFAAS, respectively, depending on concentration levels. While, due to air filters, a significant increase of some analytes mobility in individual fractions has been observed in case of the jet-milled PM (tunnel Letna), but in case of the PKC sample such effect was not found. The analyte impurities built in some filters has been tested, and the impact on the reliability of analyte results has been discussed. The arsenic species occurrence and their stability in presence of air filters (size 47 mm) were investigated in both urban PM samples as well, using HPLC-ICP-MS technique. Water soluble and by three-step BCR procedure extractable arsenic forms are shown in chromatograms